Aiming at the factors affecting the experimental results when the pycnometer measures the density of irregular small solids, this paper introduces the influencing factors and discusses the error caused by the analysis factors to the experimental results. In the operation of thermal and mechanical experiments, one of the experimental items is to use the pycnometer method to test the density of irregular solids. When students are doing this experiment, how much is the amount of irregular solids put into the pycnometer? What problems should be paid attention to in the measurement, the influence of the air bubbles attached to the surface and the pores in the interior on the experimental results, etc. are not clear. Now we will discuss several factors that affect the experimental results in the experiment.